This change was originally started by capn@, which added texture
sampling to the Triangle benchmarks. I finished up this change with the
following changes and fixes:

* Implement a correct fill texture to white using copyBufferToImage.
* Add Buffer class to wrap vk::Buffer and vk::DeviceMemory.
* Add support for using a VK_EXT_headless_surface Window, which is the
default on non-Windows platforms for now. On Windows, can be forced to
use this by defining USE_HEADLESS_SURFACE = 1.
* Fix out of bounds access because renderPassBeginInfo.clearValueCount
was set to 2 instead of 1.
* Fix illegal access to destructed ArrayRef in call to
commandBuffers[i].bindVertexBuffers.
* Make it build and run on Linux (fix compilation errors and use
aforementioned headless surface mode)

Bug: b/176981107
Change-Id: If82496315e77a062c024766863a1ca01e6b424f9
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51668
Kokoro-Result: Antonio Maiorano <amaiorano@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>